1. Field of the Invention
The present invention relates to communication systems, and more particularly to radio frequency communications between the two or more distant users via a radio frequency transponder or payload that is attached to a satellite orbiting the Earth.
2. Background Art
In conventional three axis communications spacecraft the radio frequency transponders (or "the payload") on the spacecraft consist of a receiving reflector antenna (usually a shaped reflector) that forms the radiation pattern for reception of electromagnetic signals. The received signals are amplified with a low noise amplifier and then are frequency converted to the transmit frequency. The frequency converted signals are passed through a demultiplexer that separates the various received signals into their respective frequency bands. The separated signals are amplified by traveling wave tube amplifiers (TWTAs), one for each frequency band and are combined in a multiplexer to form the high power transmit signal--the high power signal is passed through a transmit reflector antenna (usually a shaped reflector) that forms the transmit radiation pattern.
The large heat dissipating equipment (i.e. the TWTAs and multiplexer) in the transponder are usually located in the spacecraft bus on the north and south thermal radiating panels of the spacecraft. The transmit and receive reflector antenna are usually deployed outboard from the east and west sides of the spacecraft bus.